| 1. |
- Davis, M.H., et al.
(author)
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Does semantic context benefit speech understanding through top-down processes? Evidence from time-resolved sparse fMRI.
- 2011
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In: Journal of cognitive neuroscience. - : MIT Press - Journals. - 0898-929X .- 1530-8898. ; 23:12, s. 3914-3932
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Journal article (peer-reviewed)abstract
- When speech is degraded, word report is higher for semantically coherent sentences (e.g., her new skirt was made of denim) than for anomalous sentences (e.g., her good slope was done in carrot). Such increased intelligibility is often described as resulting from “top–down” processes, reflecting an assumption that higher-level (semantic) neural processes support lower-level (perceptual) mechanisms. We used time-resolved sparse fMRI to test for top–down neural mechanisms, measuring activity while participants heard coherent and anomalous sentences presented in speech envelope/spectrum noise at varying signal-to-noise ratios (SNR). The timing of BOLD responses to more intelligible speech provides evidence of hierarchical organization, with earlier responses in peri-auditory regions of the posterior superior temporal gyrus than in more distant temporal and frontal regions. Despite Sentence content × SNR interactions in the superior temporal gyrus, prefrontal regions respond after auditory/perceptual regions. Although we cannot rule out top–down effects, this pattern is more compatible with a purely feedforward or bottom–up account, in which the results of lower-level perceptual processing are passed to inferior frontal regions. Behavioral and neural evidence that sentence content influences perception of degraded speech does not necessarily imply “top–down” neural processes.
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| 2. |
- de Frias, Cindy M., et al.
(author)
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Influence of COMT Gene Polymorphism on fMRI-assessed Sustained and Transient Activity during a Working Memory Task
- 2010
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In: Journal of cognitive neuroscience. - Cambridge, Mass. : MIT Press. - 0898-929X .- 1530-8898. ; 22:7, s. 1614-1622
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Journal article (peer-reviewed)abstract
- The catechol O-methyltransferase (COMT) gene-encoding an enzyme that is essential for the degradation of dopamine (DA) in prefrontal cortex (PFC)-contains a single nucleotide polymorphism (val/met) important for cognition. According to the tonic-phasic hypothesis, individuals carrying the low-enzyme- activity allele (met) are characterized by enhanced tonic DA activity in PFC, promoting sustained cognitive representations in working memory. Val carriers have reduced tonic but enhanced phasic dopaminergic activity in subcortical regions, enhancing cognitive flexibility. We tested the tonic-phasic DA hypothesis by dissociating sustained and transient brain activity during performance on a 2-back working memory test using mixed blocked/event-related functional magnetic resonance imaging. Participants were men recruited from a random sample of the population (the Betula study) and consisted of 11 met/met and 11 val/val carriers aged 50 to 65 years, matched on age, education, and cognitive performance. There were no differences in 2-back performance between genotype groups. Met carriers displayed a greater transient medial temporal lobe response in the updating phase of working memory, whereas val carriers showed a greater sustained PFC activation in the maintenance phase. These results support the tonic-phasic theory of DA function in elucidating the specific phenotypic influence of the COMT val(158)met polymorphism on different components of working memory.
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| 3. |
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| 4. |
- Guterstam, A, et al.
(author)
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The invisible hand illusion: multisensory integration leads to the embodiment of a discrete volume of empty space
- 2013
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In: Journal of cognitive neuroscience. - : MIT Press - Journals. - 1530-8898 .- 0898-929X. ; 25:7, s. 1078-1099
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Journal article (peer-reviewed)abstract
- The dynamic integration of signals from different sensory modalities plays a key role in bodily self-perception. When visual information is used in the multisensory process of localizing and identifying one's own limbs, the sight of a body part often plays a dominant role. For example, it has repeatedly been shown that a viewed object must resemble a humanoid body part to permit illusory self-attribution of that object. Here, we report a perceptual illusion that challenges these assumptions by demonstrating that healthy (nonamputated) individuals can refer somatic sensations to a discrete volume of empty space and experience having an invisible hand. In 10 behavioral and one fMRI experiment, we characterized the perceptual rules and multisensory brain mechanisms that produced this “invisible hand illusion.” Our behavioral results showed that the illusion depends on visuotactile-proprioceptive integration that obeys key spatial and temporal multisensory rules confined to near-personal space. The fMRI results associate the illusion experience with increased activity in regions related to the integration of multisensory body-related signals, most notably the bilateral ventral premotor, intraparietal, and cerebellar cortices. We further showed that a stronger feeling of having an invisible hand is associated with a higher degree of effective connectivity between the intraparietal and ventral premotor cortices. These findings demonstrate that the integration of temporally and spatially congruent multisensory signals in a premotor-intraparietal circuit is sufficient to redefine the spatial boundaries of the bodily self, even when visual information directly contradicts the presence of a physical limb at the location of the perceived illusory hand.
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| 5. |
- Heinrich, A., et al.
(author)
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The continuity illusion does not depend on attentonal state: fMRI evidence from illusory vowels.
- 2011
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In: Journal of cognitive neuroscience. - : MIT Press - Journals. - 0898-929X .- 1530-8898. ; 23:10, s. 2675-2689
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Journal article (peer-reviewed)abstract
- We investigate whether the neural correlates of the continuity illusion, as measured using fMRI, are modulated by attention. As we have shown previously, when two formants of a synthetic vowel are presented in an alternating pattern, the vowel can be identified if the gaps in each formant are filled with bursts of plausible masking noise, causing the illusory percept of a continuous vowel (“Illusion” condition). When the formant-to-noise ratio is increased so that noise no longer plausibly masks the formants, the formants are heard as interrupted (“Illusion Break” condition) and vowels are not identifiable. A region of the left middle temporal gyrus (MTG) is sensitive both to intact synthetic vowels (two formants present simultaneously) and to Illusion stimuli, compared to Illusion Break stimuli. Here, we compared these conditions in the presence and absence of attention. We examined fMRI signal for different sound types under three attentional conditions: full attention to the vowels; attention to a visual distracter; or attention to an auditory distracter. Crucially, although a robust main effect of attentional state was observed in many regions, the effect of attention did not differ systematically for the illusory vowels compared to either intact vowels or to the Illusion Break stimuli in the left STG/MTG vowel-sensitive region. This result suggests that illusory continuity of vowels is an obligatory perceptual process, and operates independently of attentional state. An additional finding was that the sensitivity of primary auditory cortex to the number of sound onsets in the stimulus was modulated by attention.
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| 6. |
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| 7. |
- Kauppi, Karolina, et al.
(author)
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Combined gene effects on hippocampal mnemonic processing : a large-scale imaging-genetics study of APOE, BDNF, KIBRA, and CLSTN2
- 2013
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In: Journal of cognitive neuroscience. - 0898-929X .- 1530-8898. ; 25:Suppl., s. S140-S141
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Journal article (other academic/artistic)abstract
- Twin studies have revealed that memory and relatedbrain functions are highly heritable traits, but putative candidate geneshave shown small and inconsistent effects -referred to as "the missing heritability". Little is known about the combined effect of several genes onbrain function: whether the presence of one "risk" variant hides the effect ofanother, interacts with it, or increases the risk in an additive -or even multiplicative -way. In a large fMRI sample we explored the combined effect ofpolymorphisms with documented impact on brain activation in the medialtemporal lobe (MTL) during episodic memory encoding or retrieval. Analyses of the effects of individual genes revealed decreased MTL activationfor ApoE £4 and BDNF Met alíeles during encoding, and for Kibra CCand the CLSTN2 T alíele during retrieval. Analyses of combined effectsrevealed that, during encoding, carriers of both the ApoE £4 and the BDNFMet alíele had lowest MTL activation, whereas non
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| 8. |
- Koivisto, Mika, et al.
(author)
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Recurrent processing enhances visual awareness but is not necessary for fast categorization of natural scenes
- 2014
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In: Journal of cognitive neuroscience. - : MIT Press. - 0898-929X .- 1530-8898. ; 26:2, s. 223-231
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Journal article (peer-reviewed)abstract
- Humans are rapid in categorizing natural scenes. Electrophysiological recordings reveal that scenes containing animals can be categorized within 150 msec, which has been interpreted to indicate that feedforward flow of information from V1 to higher visual areas is sufficient for visual categorization. However, recent studies suggest that recurrent interactions between higher and lower levels in the visual hierarchy may also be involved in categorization. To clarify the role of recurrent processing in scene categorization, we recorded EEG and manipulated recurrent processing with object substitution masking while the participants performed a go/no-go animal/nonanimal categorization task. The quality of visual awareness was measured with a perceptual awareness scale after each trial. Masking reduced the clarity of perceptual awareness, slowed down categorization speed for scenes that were not clearly perceived, and reduced the electrophysiological difference elicited by animal and nonanimal scenes after 150 msec. The results imply that recurrent processes enhance the resolution of conscious representations and thus support categorization of stimuli that are difficult to categorize on the basis of the coarse feedforward representations alone.
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| 9. |
- Kompus, Kristiina, 1983-, et al.
(author)
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Multimodal imaging of incidental retrieval : the low route to memory
- 2011
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In: Journal of cognitive neuroscience. - : MIT Press - Journals. - 0898-929X .- 1530-8898. ; 23:4, s. 947-960
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Journal article (peer-reviewed)abstract
- Memories of past episodes frequently come to mind incidentally, without directed search. It has remained unclear how incidental retrieval processes are initiated in the brain. Here we used fMRI and ERP recordings to find brain activity that specifically correlates with incidental retrieval, as compared to intentional retrieval. Intentional retrieval was associated with increased activation in the dorsolateral prefrontal cortex. By contrast, incidental retrieval was associated with a reduced fMRI signal in posterior brain regions, including extrastriate and parahippocampal cortex, and a modulation of a posterior ERP component 170 ms after the onset of visual retrieval cues. Successful retrieval under both intentional and incidental conditions was associated with increased activation in hippocampus, precuneus and ventrolateral prefrontal cortex, as well as increased amplitude of the P600 ERP component. These results demonstrate how early bottom-up signals from the posterior cortex can lead to reactivation of episodic memories in the absence of strategic retrieval attempts.
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| 10. |
- Kühn, Simone, et al.
(author)
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Brain areas consistently linked to individual differences in perceptual decision-making in younger as well as older adults before and after training
- 2011
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In: Journal of cognitive neuroscience. - Cambridge, Mass. : MIT Press. - 0898-929X .- 1530-8898. ; 23:9, s. 2147-2158
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Journal article (peer-reviewed)abstract
- Perceptual decision-making performance depends on several cognitive and neural processes. Here, we fit Ratcliff's diffusion model to accuracy data and reaction-time distributions from one numerical and one verbal two-choice perceptual-decision task to deconstruct these performance measures into the rate of evidence accumulation (i.e., drift rate), response criterion setting (i.e., boundary separation), and peripheral aspects of performance (i.e., nondecision time). These theoretical processes are then related to individual differences in brain activation by means of multiple regression. The sample consisted of 24 younger and 15 older adults performing the task in fMRI before and after 100 daily 1-hr behavioral training sessions in a multitude of cognitive tasks. Results showed that individual differences in boundary separation were related to striatal activity, whereas differences in drift rate were related to activity in the inferior parietal lobe. These associations were not significantly modified by adult age or perceptual expertise. We conclude that the striatum is involved in regulating response thresholds, whereas the inferior parietal lobe might represent decision-making evidence related to letters and numbers.
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